Lifestyle behaviors such as increased private car use, stress, low physical activity, and unhealthy eating negatively affect individual and global health, environment and economy. We must change behavior, not only to decrease suffering and economical costs, but to promote wellbeing for flourishing human beings on a living planet. It may not be simple to change ingrained behaviors. Nevertheless, with aid from interventions, the success rate for behavioral change is high, yet not automatically lasting. Despite growing harm, and that brief change generates brief effects, research on maintained intervention-induced behavior is scarce. Due to this research gap, this thesis aims to broaden understanding of psychological mechanisms involved in health- and lifestyle-related intervention-induced behavior and maintenance and suggest potential development for intervention initiators and participants. The aim is approached through three field studies: Study I uses a quantitative approach to investigate motives for intervention participation, as well as psychological mechanisms in early phases of behavior adoption, in relation to immediate behavior change in a travel-intervention setting using incentives. Study II uses a quantitative approach to investigate psychological mechanisms in adopting and maintaining behavior in a mandatory, wellbeing intervention setting. Study III uses a mixed-methods approach to investigate psychological mechanisms on a deeper level, in a fee-based lifestyle intervention. For maintained intervention-induced behavioral change, the main findings indicate the importance of: Focusing on behavior goals; undergoing positive experiences during an intervention; experiencing gains from immediate outcomes; and learning to apply a flexible approach that meets shifting conditions and responses through the different intervention phases.

The present field study investigates the reduction of car use through a voluntary travelbehavior intervention program that provides participants with temporary free publictransportation. Three factors – self-efficacy, social support and satisfaction – have previ-ously been shown to be important for behavior change during physical activity interven-tion programs. In travel behavior interventions, however, these factors have often beenstudied individually and less is known about their combined effects on travel behaviorchange. Furthermore, while motives for participating in travel behavior interventions havebeen frequently studied within travel behavior interventions research, there is a lack ofstudies investigating the influence of motives on travel behavior change. To better under-stand the importance of different motives as well as the importance of self-efficacy, socialsupport, and satisfaction with travel on behavior change, a series of surveys were admin-istered to 181 participants before, during, and after their participation in a voluntary travelbehavior intervention. The results show that greater self-efficacy and social support duringthe intervention led to greater travel behavior change. These results indicate that in orderto gain better results from travel behavior interventions, individuals should be helped toincrease their travel-related self-efficacy, and significant others should be involved to pro-vide social support. We discuss possible ways of accomplishing this.

The household plays an important role in behavior change in many lifestyle areas. Various intervention programshave been implemented in order to change travel behavior and it is well known that travel behavior is influenced bythese, and that the household plays an important role. Less research has gone into understanding the reasons forsuch behavior changes. With the aim of understanding more about household influences and triggers of travelbehavior change, two intervention studies were conducted which included free travel passes on public transport. InStudy 1 (n=108) questionnaires were sent out by e-mail to investigate whether or not household members’ influenceanother member participating in a voluntary change program, and to thus identify influential triggers. In Study 2(n=20), interviews were conducted to identify and understand influential triggers in travel behavior change. The resultsshow, in line with previous research, that household members influence each other’s behavior. In addition toinstrumental triggers, affective triggers were also identified as being of key importance. Although the householdenabled travel behavior change, it was predominantly perceived to hinder travel behavior change.

Is it possible to help students experience increased well-being that proceeds by volitional actions from mandatory participation in interventions? The aim of this field study was to better understand the influence of expectancy, motivation, and well-being experiences during a positive activity intervention on long-term behavior change and long-term well-being. The study included 59 students enrolled in a course that included choosing a positive activity that they would plan for and implement in their lives for 6 weeks. The participants answered questionnaires before (pre-measure) and after the intervention (short-term measure), as well as an unannounced follow-up questionnaire 6 months later (long-term measure). Overall, the results indicate the importance of coexisting intrinsic motivation and high expectancy in the outcome and that the key driver of sustained volitional behavior change and experiencing long-term increased well-being is to experience increased well-being during the intervention. The results of the study show that it is possible to help students experience increased well-being that proceeds by volitional actions. The study shows that a mandatory positive activity intervention, including free choice of activity and course of action, can induce new long-term behaviors and long-term increased well-being.

The aim of this mixed methods field study was to gain a better understanding of how psychological factors can contribute to success in intervention-induced behavior change over time. While it can be difficult to change behavior, the use of interventions means that most participants succeed in change during the intervention. However, it is rare for the immediate change to automatically transform into maintained behavior changes. Most research conducted on health-related behavior change interventions contains quantitative studies that investigate key intervention components on a group level. Hence, to bring more knowledge about maintained intervention-induced behavior change, there is need for a study approach that enhances the understanding of individual participants' experiences during and after the intervention. Therefore, the present study, which was conducted in Sweden, used a mixed methods design (triangulation) consisting of pre-, post-, and follow-up quantitative data (questionnaires and body measurements) and qualitative data (interviews), where the individuals' accounts are used to broaden the understanding of the intervention and the behavior change process. All study participants were enrolled in a volitional (fee-based and non-manipulated) intervention given by certified gyms. The quantitative data collection included 22 participants who completed questionnaires and body measurements before and after the intervention, plus 13 complete body measurements 6 months after the intervention. The qualitative data included pre-interviews with 12 participants and six follow-up-interviews. The questions in both questionnaires and interviews related to expectations, efficacy, motivation, goals, achievements, behavior change, and future. Overall, the results show that levels of expectations, efficacy, and motivation cannot be used in isolation to predict maintained intervention-induced behavior change. To successfully extend and maintain immediate change, it was crucial to experience goal achievement (but not BMI change). Furthermore, enabling talk was salient in the pre-interviews with participants reporting successful immediate (and maintained) change. By contrast, pre-interview disabling talk turned out to be evident in interviews, with participants not responding to follow-up. When the qualitative and quantitative results are summarized and integrated, it appears that subjective goal achievement, combined with enabling self-talk, were crucial factors in successful maintained behavior change.